package QualificationRound.Sum;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

public class Bate2
{
	private static BufferedReader br = new BufferedReader(
			new InputStreamReader(System.in));

	public static void main(String[] args) throws IOException
	{
		String str = "";
		while ((str = br.readLine()) != null)
		{
			if (str.equals(""))
				continue;
			int num = Integer.parseInt(str);
			System.out.println((1 + num) * num / 2 + "\n");
		}
	}
}
